I agree with the first post.
There are actually a kind of people that are referred to as Aryans. However, many of these people are not the sort that Hitler would have called Aryan. In fact, the Aryans are originally from India.
So Hitler essentially used the word "Aryan" to refer to something that he made up. In Hitler's racial terminology, Aryans were the only people who could actually create a true civilization. He believed that all civilizations had been created by these Aryans who roamed around Eurasia creating civilizations. In modern times, Aryans had settled in Northern Europe. As the first answer says, they tended to be blonde and blue-eyed. They lived in places like Germany, the Scandianavian countries, Holland and England.
There are many interpretations of what the Aryans, in the context used by Hitler meant. One is that Hitler considered people who had a fair skin, blond hair and blue eyes as the Aryans. They were the direct ancestors of the true Germans and constituted a master race which had descended from the divine whereas others races had evolved from the apes. They were supposed to be physically as well as culturally superior to all the other races. Hitler hated the Jews, and the Slavic peoples, like the Czechs, Poles, and Russian as they were considered an inferior race which was trying to stop the original Aryans from increasing their number. Hence he believed they degraded the superior status of the Aryans.
Aryans that Hitler referred to were supposed to be a race of people from ancient civilizations, who migrated east and southwards from central Asia and spread to all parts of Indian Subcontinent. These people were supposed to have more advanced civilization as compared to the civilization of people had been living in the Indian subcontinent from earlier times. Thus the highly developed ancient Indian civilization is attributed by many expert to the superior civilization of the Aryans who migrated to Indian subcontinent.
Since the time of Hitler many new historical evidence have come to light that does put question marks on the theory that credits the invading Aryans totally for the superiority of Indian civilization. However at the time of Hitler, Aryans did enjoy a reputation of being people of very high caliber. Also as per the limited historical evidence available then, it was not difficult for Hitler to distort fact and claim that, Aryans who migrated to Indian subcontinent belonged to the same race that later formed the population of supposedly original Germans. To emphasize the links with the Aryan civilization, Hitler adopted the symbol of swastika, which is an incorrect copy of a symbol with the same name used widely by Indians. In this way Hitler tried to create a feeling among Germans that they were superior to the people of other European countries, and to the Jews who were supposed to be non-Aryans.
Hitler believed that he and the members of the Nazi party were of the 'Aryan' race. This was believed by him to be the perfect human specimen, characterized by features such as blonde hair, blue eyes, and excellent health.
His use of the word Aryan, however, is incorrect. See the reference link for information about the real Aryan people.